Modern computer systems require large amounts of non-volatile, inexpensive data storage. Typically the best candidate for such storage has been magnetic disk drive systems. A disk drive stores data in the form of magnetic transitions representing bits of data. The magnetic transitions form concentric tracks of data on the surface of a magnetic disk. These tracks of data are written onto the disk and read from the disk by a magnetic head incorporated on a slider. The read head usually includes a read element such as a giant magnetoresistive sensor (GMR), although various other sensors such as tunneling magnetoresistance sensors (TMR) have also been investigated. This read element is disposed between a pair of shields, constructed of a soft magnetic material, which acts to prevent the detection of stray magnetic fields. The head also includes an inductive write element. Details of the construction of read and write elements will be discussed in greater detail below. The slider is attached to a suspension and to an actuator that moves the slider over the disk to read and write the various tracks of data on the disk. As the disk spins, air immediately adjacent to the disk move with it due to viscous forces, allowing the slider to fly over the disk on a very small cushion of air. The surface of the slider immediately adjacent to the disk, referred to as an air bearing surface (ABS), has a shape which facilitates the slider's flight over the surface of the disk by regulating air pressure at various point under the slider. The magnetic heads generally are disposed at the trailing edge of the slider, extending toward the air bearing surface.
Sliders are manufactured on wafers, with many thousands of sliders being produced on a single wafer. The read and write element of each slider is formed on top of the wafer using various material deposition and photolithographic processes that will be familiar to those skilled in the art. With reference to FIG. 1, the wafer is sliced into rows 100 each containing many sliders. This level of the manufacturing process is generally referred to as the “row level”. It is at this level of manufacture that the (ABS) 102 is generally formed. The side of the row 102 that is to become the ABS of the various sliders is carefully lapped to remove a desired amount of material. The amount of material removed must be carefully controlled, because it will ultimately determine the stripe height of the sensor, (ie the distance from the ABS edge of the sensor to the back edge of the sensor. Careful control of stripe height is critical to sensor performance. After the lapping process has been completed, the row is sliced into individual sliders as indicated by dashed lines in FIG. 1.
With reference to FIG. 2, which illustrates a top down view of a row at read element level, prior art ELGs 201 have been incorporated along side read elements 203 in a row 205. Removal of material from the ELG 201 during lapping increases the resistance of the ELG 201. By measuring this resistance change an operator can determine the proper point at which to cease lapping. As can be seen, such a method of monitoring lapping takes up valuable space on the row 205. This space could otherwise incorporate sliders, which would greatly increase the number of sliders formed on a given wafer. It will be appreciated by those skilled in the art that a write element (not shown) would typically be constructed above the read sensor and the row would be sliced into sliders as previously discussed.
In an alternate form of sensor, termed a recessed sensor, the sensor is recessed a predetermined distance from the ABS. This can be advantageous in that the lapping process does not lead to smearing of the sensor. When manufacturing a recessed sensor, the lapping process does not determine the stripe height, as this is defined earlier by lithographic processes. However, careful control of the lapping process remains critical because it determines the distance from the ABS to the sensor and therefore, determines the sensitivity with which the sensor can detect magnetic fields. In other words, the lapping process must remove enough material so that the sensor is not too far from the ABS (less than 10 nanometers), but cannot remove so much material that the sensor is exposed.
FIG. 3 describes a prior art method, also disclosed in co-pending, commonly assigned patent application Ser. No. 10/666,679 filed Sep. 19, 2003, for monitoring the amount of material removed during a lapping operation. This method has been proposed for constructing a recessed sensor. FIG. 3 depicts a cross section of a slider during the lapping process. The row level 301 of the wafer is formed with a conductive portion 303, formed of the same material as the sensor 305. The conductive portion 303 and sensor portion 305 are separated by a non-conductive material 307, which can be for example alumina. The non-conductive portion 307 can be formed by removal of sensor material and refilling with non-conductive material. As the slider is lapped, the resistance of the conductive portion 303 is measured. When the conductive portion 303 has been completely removed, the resistance increases essentially infinitely. When this increase in resistance is detected, the lapping process is stopped and a second method of lapping control is employed. With the resistive lapping guide 303 removed further lapping monitoring requires applying a magnetic field and measuring the increase in GMR as lapping progresses. As will be appreciated by those skilled in the art, such a technique for monitoring further lapping progress can be time consuming and difficult to control.
Therefore, there remains a need for an ELG that can allow lapping to be accurately monitored in either a recessed or exposed sensor design. Such a method would preferably utilize already existing processing steps rather than adding process complexity. Further such a technique would not occupy valuable wafer area, which could otherwise contain sliders.